The Sony MEX-1HD is an awesome head unit! It has a 10GB hard disk built-in. This means that you can
store approximately 2000 ATRAC3 tracks on the unit, so you won't ever need to
store all those CDs in the car. It is also striking with its Iridium
finish.

Features

There are many MP3-capable head units on the market, but few can store
songs in the head unit itself. The 1HD allows you to move songs from a
Memory Stick, or from a Walkman directly to the Hard Disk (HD) built into
the unit, which are then converted to ATRAC3 format (for copy protection
purposes).

If
you haven't already encoded your music in MP3 format on a computer, don't
worry. Pop in a regular audio CD and the unit will encode the CD to the
internal drive in Sony's ATRAC3 format. The unit can rip CDs to the HD
faster than real speed. In my experience the encoding time was about 10-15
seconds per track. In other words, you can put in your CDs one after the
other, encode them to ATRAC3 right in the 1HD, and you are done.

You can only play MP3 files from CD-Rs that you make
on some other component, such as your computer.

When you Rip from CD on the 1HD, files are encoded
onto the 1HD hard drive in
the ATRAC3 Copyright Protection Format.

The ATRAC3 format has copyright enforcement.
Definitely read the manual on the rules.

The unit has a USB connection, but this
connection is a controller connection, not a device connection. This
means that you cannot connect a laptop to it and move files back and
forth. You can however connect another Sony USB enabled device and move
ATRAC3 files.

The 1HD doesn't play Windows Media Format
(*.wmv) files.

Some
of you may notice right off the bat that the display on this device is
very large. To insert CDs and to access the memory slot, the motorized
face drops out of the way.

This
is not a slot-load CD player. The G-Protection tray is more like your
computer CD player. Press the eject button and the tray opens, press it
again and it closes. Note that, although you can see there is a CD-R/RW
logo on the drive drawer, it will not record CD-Rs by itself (at least
there is nothing in the instruction manual about it).

Speaking of G-Protection, I thumped the unit hard enough that any regular
CD player would have lost the track entirely. The shock protection system
on the 1HD can refocus the laser after losing the track in 0.5 seconds.
Even after the pickup loses the track, the buffer continues to play until
the track is re-focused. So, you hear no loss in music continuity. Very effective.

The unit offers a 7 band EQ in addition to
the regular +10dB/-10dB Bass and Treble adjustments. The 1HD allows
you to specify cutoff frequency for the main speakers, a handy feature.
With the 1HD you can also specify the cutoff frequency for the subwoofer.
These two features coupled together mean that there is no need for an
external crossover when driving external amplifiers. That's money saved
that you can spend on other components.

Sound Quality

Above is the measured frequency response of the CD
portion of the player, using regular 16/44 tracks. This measurement was taken from the RCA outputs.
You can see that the player exhibits a very flat response to 5 kHz, where it
rolls off to -6 dB at 20 kHz. (A loop-through test with just the computer sound
card that we use to measure response is flat to 20 kHz.)

We measured a THD of
0.037% using a 1 kHz sine wave recorded at 16/44. Overall, the player sounded very good. All measurements were taken
from a 12v bench source to rule out induced noise from the vehicle's
electrical system. Sony specs the 1HD S/N at 90 dB. I usually feel more comfortable with 100 dB or
better.
The unit spikes 10 dB - 15 dB when changing the volume, lending a little more
noise. At 0 dB (its highest volume), there was no clipping.

Usability

My favorite feature of the unit is the dual
knobs. This allows you to control the unit without ever taking your eyes
off the road. The knobs have detents, so it's easy to tell physically when
you have changed the volume or selections.

Music is sorted into folders on the hard drive, and CD information is used to automatically name files. There is a
hierarchical nature to the folder structure, for example:

Folder Name: Rock

CD 001: Eagles Greatest Hits

Track 001: Hotel California

As you can see, this layout makes it easy to
navigate 2,000 tracks. Again, the knobs are a gift when you have to enter in
a track name by hand. The CD Rip feature and CD naming really help when
encoding CDs to the HD.

The 1HD also has auxiliary inputs. This
allows you to connect satellite navigation, or extra audio devices directly to
the unit. The aux input is controllable with the volume knob as well.

MP3-Encoded Audio Performance

I encoded my test CD at the highest bit
rate, then measured the resulting frequency response and THD. The results
indicate that they are almost
identical to the CD performance.

The 6 dB rolloff at 20 kHz is there, suggesting that
the frequency response is independent of encoding for this product. I verified this using the
aux inputs, and it also generated a -6 dB curve.

THD with MP3s was higher than with 16/44 CD, but that
is to be expected. Although 0.07% is a pretty respectable number for
a compressed track, it is probably still somewhat audible, but this is the
price that one pays for MP3 compression.

Conclusions

Overall, the Sony MEX HD1 Head Unit is very special. There is a small disadvantage in that this unit will
not allow you to store MP3 files on its HD, but if you don't already have
a large MP3 collection, this wouldn't be of any significance. The HD1 is
beautiful, sounds great, and has more features than you would imagine. Highly recommended!